1. Field of the Invention
The present invention relates to a metallic carrier base material for maintaining the catalyst for exhaust gas purification to be used generally by mounting in the middle of an exhaust gas pipe as a means to purify the exhaust gas of automobiles. Here, the "carrier base material" differs from the "carrier" as used in the field of chemistry' it means an implement used to maintain the catalyst supported by the carrier.
2. Description of Prior Art
In order to enlarge the carrier area per unit volume, i.e. to enlarge the effective contact area between the exhaust gas and the exhaust gas purification catalyst per unit volume, and to ensure the lightweight design for the metallic carrier base material itself, the metallic carrier base material has conventionally consisted of a multi-layer body of spiral or hierarchical form with a number of screen-like vent holes which pass exhaust gas in a certain direction. The planar band materials and the corrugated band materials are made of very thin heat-resistant steel strips of less than 0.1 mm in thickness, and are piled up alternatively to furnish the contact portion. The metallic carrier base material, composed of such multi-layer body material, is accommodated in a metal case with open ends when necessary. The bonding between the band materials themselves in the contact portion of the multi-layer body, or between the band material and the metal case, is performed by brazing, after the formation of the multi-layer body by electron beam welding or laser welding. This is described in the Japanese providional Patent Publications Nos. 54-13462, 57-1585, 56-4373, etc. Alternatively, bonding is performed by treating the band materials in advance with the brazing material of powdery or foil types.